1. Field of the Invention
The present invention relates to the technology for preventing unauthorized copying of the contents recorded on optical discs such as a digital versatile disc (DVD), a compact disc (CD), and the like.
2. Description of the Related Art
Recently, as CDs and DVDs have been rapidly developed, huge amounts of music software, video software, and computer software, and the like have become widely available as the contents of such optical discs. This has raised concerns about unauthorized copying of the contents. Thus, copy protection by e.g. encrypting the contents on the media has been proactively employed as a measure to protect copyrights.
In conventional optical discs such as CDs, DVDs, or the like, disc control information needed for reproduction of the contents of the discs is recorded on the discs themselves along with the contents of the discs. Even if content information recorded on the discs is encrypted, it can be extracted as encrypted content information. Consequently, if a decryption key is cracked, the contents may be easily decrypted.
Meanwhile, contactless IC cards employing noncontact communication technology have been recently put to practical use. Such a contactless IC card uses e.g. a radio frequency identification (RFID, which is a noncontact automatic identification technology by a radio frequency) chip for storage of data associated with the card. Including the contactless IC card using the RFID chip, RFID tags, which are microminiature, allow data recorded therein to be read in a noncontact manner, and are configured to work without a battery, are expected to be increasingly utilized in the future.
To take advantage of the features of the RFID tag that it is microminiature, allows recorded data to be read in a noncontact manner, and works without a battery, it has been proposed to combine the RFID tag with an optical disc such as a CD or a DVD so as to prevent unauthorized copying of the content of the optical disc. For example, Japanese laid-open patent publication 2003-187524 discloses a system in which an RFID chip is embedded in an area on a digital recording medium such as a CD or a DVD where the content, which is encrypted, of the medium is not recorded, and the encrypted content in the content recording area is decrypted by using a decryption key recorded in the RFID chip for reproduction. Japanese laid-open patent publication 2002-373029 discloses a method of preventing unauthorized copying of software for use in a personal computer. The method includes: embedding, in an optical disc containing encrypted software, an RFID tag containing a decryption key for decrypting the encrypted software; and decrypting the encrypted software with the decryption key recorded in the RFID tag at the time of installation of the software.
However, the method of preventing unauthorized copying of the contents recorded on optical discs with the use of cryptographic technology as described above has the following problem. As computers become faster and more sophisticated with technological advances, a possibility may arise that the encryption is cracked. Consequently, the conventional method cannot reliably prevent unauthorized copying of the contents recorded on optical discs.
Further, as one of services to be provided to users with the content recorded in the optical disc as described above, it is known to provide a “bonus content” (a content added to basic contents, e.g., a piece of music that is arranged and not played in a typical concert) that is recorded in a “bonus track”. Users that are allowed to view or listen to the bonus content should be limited to those having legally purchased the optical disc on which the bonus content is recorded.